Field
The present disclosure relates to optical communication equipment and, more specifically but not exclusively, to transmission and/or detection of optical polarization-division-multiplexed (PDM) signals.
Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
An optical PDM signal is typically generated at an optical transmitter by separately modulating two optical waves having orthogonal polarizations and combining the resulting two modulated optical waves using a polarization-beam combiner. The resulting combined optical wave is then coupled into an optical fiber for transmission to an optical receiver. Birefringence in the optical fiber, which depends on the environmental factors, such as temperature and mechanical stress, typically causes the polarization state of the optical PDM signal to change along the propagation path. As a result, when the optical PDM signal arrives at the optical receiver, its polarization state is different from what it was at the optical transmitter. To recover the data carried by the received optical PDM signal, the optical transmitter is typically configured to use a combination of coherent (e.g., homodyne or intradyne) detection and polarization rotation. The polarization rotation may be applied by means of a polarization controller in the optical domain or a digital signal processor in the electrical domain.